Pregnant women who smoke cigarettes at the time they become pregnant and who register with a private collaborating obstetrician before their 16th week of pregnancy will be randomly allocated to a treatment group who will be asked to actively participate in a smoking cessation program to quit smoking and a control group who will receive anti-smoking advice from their health providers. Mean birth weight of the two groups of infants will be compared to determine if smoking during pregnancy is a causal factor in low birth weight.